The present invention relates to a thin film optical device for optical communication, optical data processing or the like, and more particularly to an optical switch for deflecting a light beam introduced into an optical waveguide film having a thickness substantially equal to a light wavelength so as to switch a propagating of the light beam.
Prior thin film optical switches which have thus far been proposed are of the type using an electro-optic effect or an acoustic-optic effect. Those devices deflect the guided light beam through a diffraction grating formed in an optical waveguide film by the electro-optic effect or the acoustic surface wave. More specifically, interdigital electrodes are provided on a thin film waveguide made of, for example, an electro-optic crystal LiNb.sub.x Ta.sub.1-x O.sub.3 in the LiNbO.sub.3 system. A diffraction grating is formed by an electro-optic effect which is developed in accordance with a voltage applied to those electrodes so as to deflect the guided light beam. Alternatively, an acoustic surface wave is propagated through a Ta.sub.2 O.sub.5 film as a waveguide film deposited on a piezo-electric crystal such as quartz, for example, a Y-cut .alpha.-quartz. The diffraction grating thus formed by the acoustic surface wave propagating through the waveguide film diffracts the guided light beam, so that the guided light beam is deflected. In these optical switches, one of the most important characteristics is a deflection angle of the light beam, and it is desirable that the deflection angle is large, since a very long waveguide is required to obtain a sufficient crosstalk requirement in case of a small deflection angle. A deflection angle obtained by the above-mentioned diffraction grating type optical switch is 2.degree. or less at the most. This small deflection angle is a great problem as far as an optical switch element is integrated. In the diffraction grating type optical switch, the shorter the grating period, the larger the deflection angle. Consequently, it is necessary that an optical switching device utilizing the electro-optic effect is designed as to have interdigital electrodes with a grating period equal to that of the diffraction grating. In order to realize this interdigital electrode, an electrode pattern must be formed with a high accuracy in the order of submicron, which therefore requires highly advanced techniques for fabricating a precise electrode pattern. In the optical switching device utilizing the acoustic surface wave, it is necessary to generate a surface acoustic wave having a frequency of several hundreds MHz or more. It follows that there are needed highly sofisticated peripheral devices such as a transducer with a high efficiency for producing ultrasonic wave, a high frequency oscillator or the like. Thus, these conventional switching device of diffraction grating type has a drawback that a manufacturing cost is high in addition to the above-described disadvantage of a small deflection angle.
Another switching device was proposed by S. K. Sheem et al. in Applied Optics Vol. 17, No. 6, p. 892 (15 March 1978) "Light beam switching and modulation using a built-in dielectric channel in LiNbO.sub.3 planar waveguide". In this proposal, a pair of stripe electrodes are oppositely disposed with a proper distance on a thin film waveguide of electro-optic crystal, e.g. a Ti diffused LiNbO.sub.3 thin film waveguide. When a predetermined voltage is not applied across these electrodes, the guided light beam propagates straightly through a waveguide region or channel between the electrodes. When the voltage is applied across the electrodes, the electro-optic effect reduces a refractive index in the waveguide region between the electrodes to totally reflect the guided light beam so that the light beam is deflected. However, the deflection angle obtained by the switching device is 12.degree. at most and therefore the deflection angle still involves great problems in case of the fabrication of an optical switch in the form of an optical integrating circuit.
In U.S. Pat. No. 3,589,794 entitled "Optical circuits", there is disclosed a tuning device in FIG. 19, in which a dielectric chip disposed on a waveguide is moved vertically or horizontally with respect to the waveguide to control a coupling between a figure-eight resonator disposed in the proximity of the waveguide and the waveguide. While in this U.S. Patent, reference is made to a change of the resonating frequency of the resonator by moving the dielectric chip, it does not disclose the change of a propagating direction of the light beam propagating through the waveguide and an improvement of increasing a deflection angle of the light beam.